The word Invertebrate describes any animal which does not have a spine. Although lacking an internal skeleton, many invertebrates make up for this by developing a shell (as with snails), or a hard exoskeleton that protects their entire body (as with lobsters and insects.) Having a shell doesn't qualify an animal as an invertebrate, however; many invertebrates are soft-bodied, relying on other ways to protect themselves from their environment. Click here for more info...